Ion exchange process for separating the rare earths



M. M. WOYSKI Jan. 26, 1965 ON EXCHANGE PROCESS FOR SEPARATING THE RARE EARTHS 3 Sheets-Sheet 1 Filed May 15, 1962 lill',

QWBSS llllL TNA IN VEN TOR. I afh Woyw, BY

M. M. WOYSKI Jan. 26, 1965 ION EXCHANGE PROCESS FOR SEPARATING THE RARE EARTHS 5 Sheets-Sheet 2 Filed May 15, 1962 WNWSS INVENTOR. l Maf/C Wy/Z;

M. M. WOYSKI Jan. 26, 1965 ION EXCHANGE PROCESS FOR SEPARATING THE RARE EARTHS 3 Sheets-Sheet 3 Filed May 15, 1962 United States Patent iice 3,167,389 Patented Jan. 26, 1965 N EXCHANGE PRCESS FOR SEPARA'EENG THE RARE EAR'IHS Mark M. Woyski, West Chicago, Ill., assigner to American Potash Se lhemical Corporation, Los Angeles, Calif., a corporation of Delaware Filed May l5, 1962, Ser. No. 198,394 7 Claims. (Cl. 23-19) The present invention relates to a new and improved method of separation and purification of mixtures of rare earths which may include yttriurn. More specifically, the invention is directed to a method of continuously separating and purifying mixtures of rare earths and yttrium by ion exchange to an extent that a desired product is obtained.

This application is a continuation-in-part of my copending application Serial No. 829,416 which was filed on lul 24, 1959, and assigned to the same assignee as the present application.

It is an object of the present invention to provide a new and improved method of separating and purifying mixtures of rare earths and yttrium by which method all of the various rare earths and yttrium may be separated and purified on a commercial basis and to a high degree of purity.

A further object is to provide a new and improved method of the type described which is adapted for continuous operation including as a part thereof recovery of the eluting or sequestering agent for continuous reuse thereof, the method utilizing to advantage the selective ion exchange characteristics of rare earths and yttrium and avoiding the formation of insoluble complex compounds to a degree which would normally constitute a hindrance in the eiicient continuous operation of an ion exchange system. Still a further object is to provide a new and improved method of separating rare earths and yttrium from mixtures thereof by ion exchange, the method utilizing a new ion retainer principle which permits efficient recovery and reuse of the sequestering agent, the ion retainer principle being of a nature for adaptation and utilization in a continuously operating ion exchange system, the operation of which may be varied and controlled at will to obtain the desired degree of ion separation and purification as wel1 as selective ion separation and purication.

A further object taken in conjunction with the foregoing objects is to utilize in the ion exchange method referred to a unique ion exchange liquid medium or eluting solution which may be continuously prepared and reused without interruption in continuous operation of the basic ion separation and purification system.

An additional object of the present invention is to provide a new and improved method of recovering rare earth and yttrium ions from a waste liquor, this method utilizing certain principles of the ion separation and purification method referred to above with the recovery of the sequestering agent of the ion exchanged liquid medium for continuous reuse thereof.

Other objects not speciiically set forth will become apparent from the following detailed description of the present invention made in conjunction with the drawings wherein:

FIG. 1 diagrammatically illustrates in flow sheet form a known ion exchange system which has been modied to operate in accordance with the principles of the present invention;

FIG. 2 diagrammatically illustrates in flow sheet form an operational modiiication of the system of FIG. 1;

FIG. 3 diagrammatically illustrates in iiow sheet form product recovery by ion exchange which forms a part of the present invention;

FIG. 4 diagrammatically illustrates in flow sheet form a fractional ion exchange method which makes use of certain of the principles of the present invention; and

FIG. 5 diagrammatically illustrates in flow sheet form Waste liquor ion exchange treatment which forms a part of the present invention.

The method of the present invention includes several variable concepts of operating an ion exchange system in obtaining separation and purification of rare earth mixtures which generally include yttrium. In its preferred form, the method includes ion exchange between a bed of cation exchange resin (such as Amberlite IR-120, Rohm and Haas sulfonated polystyrene resin) and a solution of the ammonium salt of ethylenediaminetetraacetic acid or solutions of other suitable sequestering agents of the type which exhibit slight solubility in their acid form.

Heretofore, rare earth separation and purification was obtained through fractional crystallization of various rare earth salts, primarily double nitrates. This method is quite laborious and with the exception of its use in separating and purifying lanthanuni and neodymium, is commercially prohibitive in cost. Accordingly, other rare earths have not been commercially available except in very small quantities of mixtures. In this respect, one additional exception is in the case of cerium which has been subject to ready separation due to the fact that its valence can be changed.

In an eifort to improve upon the known fractional crystallization procedures, an ion exchange process was developed initially for use in rare earth determinations relating to fission research in the atomic energy field and subsequently for use in separating and purifying rare earths on a commercial basis. In developing this procedure, it was found that a cation resin is a preferred repository for rare earths and that suitable selective exchange of ions can be obtained with a solution of the ammonium salt of ethylenediaminetetraacetic acid. In describing this method, reference is made to FIG. 1 which illustrates a series of columns 1-5 containing therein ion exchange solid medium in the form of beds of cation exchange resin. By way of example, columns 1-3 would be loaded with a rare earth mixture undergoing separation and columns 4 and 5 would be loaded with copper ions. A solution of the ammonium salt of ethylenediaminetetraacetic acid would flow through columns 1-5 with the initial pH of the solution being adjusted to about 8.2. As the stability of the eluting solution with the rare earth ions increases slowly and progressively with the atomic number of the rare earths, the rare earths exchanged from the resin by the solution is richer in the heavier rare earths than the original mixture. Accordingly, a degree of separation takes place during iiow of the eluting solution through columns 1-3. When the solution carrying selected rare earths reaches the copper containing columns 4 and 5, an ion exchange reaction occurs whereby the rare earths in solution are deposited on the resin as displaced by copper ions and a copper complex solution is formed. As illustrated in broken lines in FIG. l, the copper complex solution is discarded as the copper complex cannot be readily broken to recover the sequestering agent for subsequent reuse. As the ow of eluting agent through the columns 1 5 is continued, the rare earth mixture therein moves progressively through the columns accompanied by progressively greater separation and purification until each of the rare earths is present in a more or less distinct zone on the resin. At this point the heaviest rare earth elements are at the head of the ydistinct bands or zones and the lightest elements constitute the tail zones. The method is made continuous by continually loading the tail columns with copper following movement of the rare earths bands therefrom into the next successive columns. This method provided the first workable ion ex- Y change system for rare earth separation and purilication but was found tobe generally uneconomical Yand ineffiz oneness Y cient for commercial application due to several major limitations.

The presence of the copper complex in the eluting agent (when formed from ethylenediaminetetraacetic acid at'concentrations above 0.4%) as used 'inthe earlier f ion exchange method described above created the problem of copper complex precipitation 'in the resin columnsl there is no knowneconomically feasible method for break-k ing: the copper complex formed in order to Vrecover the sequestering ragent for reuse, the cost of continuously using fresh sequestering agent addedmaterially tofthe cost ofthe nal product. ,Y

As a material improvement over the Acopper rare earths and yttriumcanbe used as their own retainer with ythe use of copper-,ions eliminated and that the rare y cycle ioni Y exchangemethod kdescribed above, it has been found that combined with the rareearths of the retainer and is delivered" into any eiiiuent liquid fstorage. In treating the eiiiuent for sequestering agent-*reuse rand retainer ions reuse, the effluent is first subjected to sequestering agent removal by mineralacid treatment resulting in sequester- VingV agent-precipitation. 'The-r precipitated sequestering agent in the form of the free acid is introduced into an ion exchange liquid medium preparation zone wherein fresh eluting solution is continuously formed by combining proper quantitiesof water with recovered and fresh sequestering agent. ,The liquid medium undergoing preparationis also subjected to ammonia ltreatment and the resultingeluting solution, upon .sequestering agent content and pH adjustment, is continously delivered into column l. The solution containing` the retainer ions is suit- 1 ably stored and is used toprepare a fresh retainer column 6 forconneetion'into the successive column system upon exhaustion of the initialretainer column 5. In preparing the newv retainer column 6, the retainer solution is merely passed therethrough in exchange with the solid medium therein resulting in theabsorption of the retainer ions by the resinous material 'with the eiiiuent from col- Y umn rbeing passed to waste. f

earths and yttrium retainer ions can be recovered by ab-V sorption on resin` and continuously reused as retainer. With this discovery, it Ahas also been found'Y that the sequestering agent can'be recovered for continuous reuse* by precipitation thereof from the .eflluent eluate` by the addition thereto of a vmineral acid. The purpose of the rare earthlretainer, band in theV methodof the present inventionY isV solely to maintain the band vlengthof the rare earths being pur-ied by removing` the rare earths'.l absorbed in the eluting solutionrby -an exchange of the n eluting agent ions with those selected to constituteA thel retainer. Recognition of advantageous use of lthe variable stabilityof the eluting agent with rare'earths of varying atomic numbers `makes this particular` method possible.

From vthe foregoing `it' will be readily appreciated that sequestering agent recovery is made possible byvutilization of selected rare earths as .a retainer. Furthermore, the'recovered. sequestering Yagent Vas well as the retainer ions ,are continuouslyreused'thus materially decreasing the Ycost of operation of the systemnot only because of reagentl recovery, vbut also because of elimination of Waste disposal problems. The waste Vfrom the column 6 undergoing preparation as a new retainer column needs little FIG. l alsol illustrates. the operation of anion exchange.

system wherein selected `.rare earths are used as a rare earthv separation and purification retainer. columns le6 includebeds of cation exchange resin-With columns 1-4 constituting lthe repository zones Vfor a rare earth mixture undergoing separation andY purication. The ion exchange `liquid medium or eluting solution is delivered into the top of column kl and flows through the successive beds of resinous material in .columns .l through 4.V During this flow ion exchange occurs in a preferen# tial sequence which, generally speaking, includes fthe Vabsorption of the rare earth ions in the eluting solution displacing the ammonium content thereof whichV combines with the resin.

A11 of the.

Vtreatment forY legal disposal and nocostly ingredients which are essential to elicient operation of the system Varelost therewith. Upon exhaustion of the initial Iretainer column 5, the fresh retainer'column is ready for connection into the system and it is' utilized to ,replacecoL umn 1 from which Ythe original mixture of rarev earths undergoing separation and purilication has been removed by continuingion exchange. Column'S then contains .distinct bands of lseparated rareearths VwhichV may be subjected tofurther purification or removed as Vfinal products dependingV uponthe extent'to which thel system has beenA operated and thev original rare earth. mixture `has undergoneseparation and purification.`

Assuming .that column 5 contains in its entirety a der.-

Vsired iinal product, FIG.v 3 illustratesfproduct removal therefrom. A suitable ion exchange liquid medium (the ammonium salt of ethylenediaminetetraacetic acid) is passed into ycolumn 5 vin reverse ow direction ,to Vfluidize the resin bed therein.Y This procedure provides vfor intimate contact'between the liquid mediuml and the solid Column 5 constitutes the retainer zone I and the resinous bed therein is arepository forselected j l heavier rareV earth elements.v By way of example, where it is desired to separateand-concentrate the lighter rare Vearths from lanthanum 4to terbium, agmixture of rare` earths fromdysprosiu'm 'to lutetium mayV constitute theretainer. Asl'the eluting agent reaches theretainer/zone ofthe cycle, further i'on exchange-'occurs whereby the retainer ions displace from the eluting solution vthe rare earths absorbed therein; Accordingly, the retainer zone is decreasedl to an extent adequate to displace the rareV earths vfrom the eluting solutionwith the 4displacement resulting in the formation Vof speciedgbands orzones of Iseparated rare earths-of varying purity. As ion'exchange' continues, Ythe yretainer zone is slowly depleted and .the

Ydeposited bands of separated rare'earths increase iny medium .for eicient ion exchange. therebetween and vcomplete productremoval from the lsolid medium. The efuentV having the `product absorbedytherein is then subjected to sequestering lagent removal Vaccomplished by uprecipitation'thereof as aresult of y mineral Aacid addition. Y .The precipitated sequestering vagent is vrecovered for subsequentuse-.andthe resulting solution constitutes the product solution. The rare -earthsl of the product solution maybe precipitated therefrom by treatingthe solution with oxalic acid with the yrare earths beingvrecoveredV Vas oxalates. Y.

To further-improve on vthe separation vand:purification method illustrated in FIG. l, it was .considered'zdesirable Vto increase the concentration of the sequestering agent in the liquid medium the complex tendsto precipitate out Vof the liquid mediumonto the solid medium thereby foul- `ing the same and reducing the efficiency of ion exchange ener/,38s

y:in the continuously operating system. Upon increasing Jthe concentration of sequestering agent in the liquid merdium it has been found that the acid complex precipitates out of the medium to a greater extent. In order to eliminate this problem and permit the use of increased concentrations of sequestering agent, it has been found that by pre-treating or pre-conditioning the liquid medium prior to use thereof by forming therein a complex rare earth salt, the formation of the acid complex is held at a minimum and the concentration of sequestering agent in the liquid medium can be substantially increased.

In general, the improved eluting solution is prepared by iirst forming a solution of the ammonium salt of ethylene-diaminetetraacetic acid yand passing the same in reverse ow direction through a resinous bed the resin of which having absorbed thereon selected rare earth elements. The reverse iiow of the solution through the resinous bed results in the bed being fluidized with adequate turbulence being created to prevent segregation of reaction products. Chemically, the eluting solution prepared in this manner includes therein the neutral salt of a rare earth complex which is freely soluble. The creation of turbulence during the preparation of the eluting agent further provides for controlling the amount of slightly soluble rare earth acid complex formed to maintain the concentration thereof in the eluting agent well lbelow the solubility limit thereof.

While the eluting agent containing the rare earth complex salt can be prepared in any suitable manner, such as by using a completely separate resinous bed on which is loaded the `selected rare earth elements, this feature can be incorporated in a continuously operating system to make use of one of the columns therein in which ion exchange has already occurred. Continuous operation of the type described is illustrated in FIG. 2. For purpose of description it will be assumed that ion exchange had continued for some time through columns 1-5 in the order described above with respect to FIG. 1. The original rare earth mixture undergoing separation has moved forward to define in these columns various areas or zones of partial sep-aration and purir'ication. When the system is initially placed into operation with the eluting solution passing into column 1, this solution has been prepared by any suitable means to include therein the rare earth cornplex salt described above. The rare earths used for this purpose will be the lighter rare earths having atomic numbers no higher than the lowest atomic numbers of the rare earths to .be separated and purified.

Following continued operation of the system, the rare earths retained in column 1 will be those displaced from the eluting solution and column 1 can eventually be removed frorn the system for use in regenerating the eluting solution as shown in FIG. 2. In this respect, the efriuent issuing from the bottom of the retainer column 5 is passed into a storage zone and then introduced into a treating zone wherein the sequestering agent is removed by mineral acid treatment. As previously described in FIG. 1, the retainer solution following sequestering agent removal is collected and continuously used to prepare column 6 as a new retainer column for subsequent replacement of column 5 in the system. The precipitated sequestering yagent is reused in the ion exchange liquid medium preparation zone and the fresh liquid medium is passed through column 1 in reverse flow direction to iiuidize the resin bed therein. Column 1 is thus stripped of the rare earth ions absorbed therein to form in the liquid medium the rare earth complex salts. The completed eluting solution is then passed into a storage zone from which it is continuously delivered into column 2, etc., to provide for continuous operation of the ion exchange system.

As previously described, the rare earth ions deposited in the tail column, which will vary as any one of the columns 1 through 6 as the system operates continuously over a substantial period of time, are the ions which are initially used and continuously reused in forming the rare earth complex salt in the eluting solution. Thus, these particular ions as well as the ions forming the retainer of the system are continuously reused. Preferably, ex cess ammonia will be used in preparing the liquid medium for stripping column 1 in FIG. 2. During the iluidizing of the resin therein to form a homogeneous mixture with the liquid medium, any appreciable formation of the acid complex is prevented by neutralization Iby basic arnrnonium hydroxide released during the reaction. In this respect, neutralization of the eluting solution is maintained and the concentration of sequestering agent used therein may be increased appreciably without acid complex precipitation during subsequent ion exchange use of the eluting solution. By Way of example, the earlier copper cycle system was limited in operation to use of eluant concentrations of about 0.4% or at most 0.8%. By forming the rare earth complex salt in accordance with the principles of the present invention, the eluant concentration may be increased to as great as 10% or even somewhat above this percentage. Preferably the liquid medium including the rare earth complex salt as prepared by backwashing column 1 in FIG. 2 will be subjected to pH adjustment prior to introduction into column 2 to adjust the pH at about 3.5, or within the range of from about 2.5 to 4.5.

The following are illustrative examples of the ion exchange method of the present invention and should not be construed as limiting thereto:

EXAMPLE I Eight columns numbered 1 through 8 and containing beds of cation exchange resin (Amberlite IR-120) were placed in series operation. Each of the columns was six inches in diameter and six feet high and contained tive feet of resin bed. The volume of resin in each bed was about one cubic foot.

Two columns were loaded with purified lanthanum by passing gallons of lanthanum chloride solution containing 20 grams of lanthanum oxide per liter through them. Excess solution was removed by washing with water. Eluting solution was prepared by circulating by reverse ow `a solution of ethylenediaminetetraacetic acid and ammonia, adjusted so that the molecular ratio of the acid to ammonia was 1:4, and in which the concentration of the acid was 26 grams per liter, until a slight excess of the sequestering agent was present. The solution was reserved in the eluting solution storage tank. The columns were washed out.

The first two columns Nos. 1 and 2, serving as retainer, were loaded with a mixture of rare earths consisting of approximately 80% yttrium, 10% dysprosium and small amounts of gadolinium, terbium, holmium, and other heavy elements, but being virtually free of lighter elements. It must be noted in this connection that yttriurn .behaves in this operation as a rare earth positioned between terbium and dysprosium. To effect this loading, five kilograms of the oxide mixture were dissolved in a small excess of hydrochloric acid, diluted to a concentration of 20 grams of oxide per liter. After adjusting the pH to 3.0, the solution was pumped through the columns and excess removed by washing with water.

The rare earth mixture to be purified consisted of praseodyrnium oxide, 50%; neodymiurn oxide, 25%; samarium oxide, 10%; and small amounts of gadolinium, cerium and lanthanum. Twenty kilograms of this mixture was dissolved in hydrochloric acid and loaded on the remaining six columns, Nos. 3 through 8, in a manner analogous to that used in preparing the retainer columns Nos. 1 and 2.

The eluting solution was now introduced and iiowed successfully through the six columns Nos. 3 through 8 undergoing purification and then through the two retainer columns Nos. 1 and 2. Ion exchange occurred over a period of 48 hours, during which time the rare earth band moved forward one column. The mixture undergoing a, terasse;

purification-'was displaced fromthe tail.colurnn'lso. 3V

and moved into .the secondcolumn No.r 4 with -the resint ous bed in the .tailcolumn No. 3, having absorbed therein, the rare earth ions of theeluting solution. The retainer ions in the lead column No. 2 `were simultaneously disy' placed and collected in the eiliuent storage tank.

The sequestering .agent was now recovered' from the liquid'efluent by adding mineral acid,-adjusting to a pH.VK

of 1 iltrating `and washing. The solution containing retainer ions was reserved. Liquid medium wasfmadc up with the recovered sequestering agent and the same was passed through the tail column No. 3, reverse how, to regenerate a new supply of eluting solution. Thel tail 'col-Q umn No.v 3, afterfbeing washed free of rare earthsY was reloaded with the Solution of retainer ions previously recovered and reserved andwas then connected inA the series atrthe head of the band. ln this way, the elution proceeded uninterruptedly and the rareearth bandmovedlforward one column every 48 hours. During each '4B-hour interval, the tail column was treated for eluting solution regeneration and was reloaded with retainerions and connected in series to form the new head of the band. y

Separation and purication continued `for twenty days,

ionseparation, v yttriurn occursnf between terbium and f dysprosium. T he following is an example of yttrium separation and purification:V

'Y' lnirAMlunn Y v The purification of yttrium was carried out by using thefractions-of Examplelll below. The operating system tothe oxidethe products had the following analyses:

at which time columns Nos. 3, 4, and 6 contained, therein,

the iinal products,praseodyminum and neodyrnium. The columns containing these products were disconnected frein the system and a fresh source of ion exchange .liquidv medium containing 5% of ethylenediaminetetraacetic acid was passed in reverse flow therethrough torstrip the same in the manner described in connection with FlG. 3 above. The product ions were removed from the product solution following sequestering agent precipitation therefrom, by the addition of oxalic acid and after ignition to the Voxide the products had the followingY analyses:

Fraction 1 Percent Y203 Dy203 About 0.l

i Y Fractions` Il, III, and IV .YZOS l 99.9 DyzOs Less than 0.1 Tb407 y LSS than 0.1

Y 1 Fraction V )T203 V V .Tbrtoq i About 0.1

It will be appreciated by one skilled in theY art that by direct elution from the columns further quantities of praseodymium and neodymium of varyingV purity may be obtained andl that-after this operationis completed, the

depleted columns can be reloaded with new mixtures forY purification without disturbing the other columns in the system and the elution again continued in the manner described.V l

The methodvof the present invention can be utilizedin separatingand purifying all of the various rare earths asl controlled by appropriate selection of the retainer ions and eluting solution, ions. Aspreviously described,y the eluting solution ions have an effective atomic number Vno higher than the lowest-etiective atomic number of the ions to be separated and purified; theretainer. ions have `an atomic number at least as high-as .thehighest `atomic numrare earth mixture. kparticular procedure: Y

FlG, 4.illustrates a system wherein partial separation andV concentration 'of various 'rare earth elements can be obtained withoutVv the use of a retainer. In this .system a singlercolumn l of resin is 4loaded witha suitable mixture of rare earths. A suitable eluting solution containing therein a selected rare earth complex salt'isv passed through-the column in ion exchangewvith lthe resin Aand the effluent is subdivided into vFractions l-4 with sui-table storage zones for eachrofthese fractions. Upon completion ofpthe partial separation and-concentration, `freshly prepared liquid medium may be y passed through column .l ingreve'rse strippingjtlow to vremove the rareearth elements initially used in forming vrthe complex salt for reuse thereof in partial separation and concentration `of a new Thefollowing is anexample. of this EXAMPLE In A single column ofr 6 inches in diameterand -10 feet in height iilled with cation exchange resin was loaded with a mixture having the Vfollowing analysis:

, Percent Yttrium f 50 VGadolinium l() Samarium,, 7 l0 ",Neodyrnium 15 Dysprosiurn plusrheavier elements 15 'ber ofV any ofthe ions to be separated andpuried. VIn this respect, it will be appreciated that the extreme ions of the series may require slight variations in the method for purification and recover thereof. Thus it may be necessary to recover the product'from the eliluent eluant following the mineral acid Vtreatment described in FIG. 3;

.It -will be understood thaton ,a commercial basis it may y be desired to separate certain Vspeciied ions Vas distinguished from separating and -purifying all `of* the various The fractions.. collected had the `following analyses:

An eluting solution vcontaining' theV complex-salt of Ilanthanum, praseodymium andcerium at a'concnetration of 5% was passed through vthe column YatY a rate of 200 mlpp'er minute.

9. Fraction IV Neodymium 85 FIG. illustrates waste liquor treatment. An ion exchange column 7 con-taining the resinous medium therein has passed therethrough a suitable Waste liquor having rare earths therein. The rare earths of the waste liquor are absorbed on the resin and after a capacity load is obtained a suitable liquid medium ion exchange solution is passed through the column in reverse iiow to strip the same. As illustrated in FIG. 5, the liquid medium following stripping is subjected to mineral acid treatment to precipitate therefrom the sequestering agent Which is reused in liquid medium preparation for subsequent operations. In this procedure there is no separation or purification of the rare earth elements removed from the column, ythe purpose being merely to recover rare earth elements from waste liquor. Obviously, the rare earth mixture recovered may then be separated along the lines previously described. The recovery procedure outlined in FIG. 5 may be used advantageously to process waste containing as little as l gram per liter or less of rare earth elements.

Actually, under certain circumstances a crude rare earth mixture can function as its own retainer. This is true in the instance where the crude mixture contains a high content of one or more of the rare earth elements. Mixtures containing high contents of yttrium are rather common and if there is a very low content of rare earths immediately adjacent yttrium in the series, the yttrium can be separated from the mixture without the use of a separate retainer. Non-retainer separation is particularly useful where partial separation is desired such as described in connection with FIG. 4 above.

The eluting solution has been described above as containing rare earth complex salts, but it is also possible to make use of alkaline earth metal ions in place of rare earth ions in the complex salt. Suitable metal ions are: calcium, barium and magnesium. Where these salts are used, the system is obtained in exactly the same manner as previously described and recovery and use of the metal ions is the same. Although in the process as described, the ammonium salts of ethylenediaminetetraacetic acid and ammonium salts of the rare earth complexes have been specied, it is always possible to replace the bulk of the ammonium ions with an alkali metal ion; namely, lithium, sodium, potassium, rubidium, or cesi-um. However, it is preferred practice to retain a nominal amount of ammonium ion in the salts as better pH control is obtained. Thus, the eluting solution may be defined as comprising an aqueous solution containing ethylenediaminetetraacetic anions.

The retainer ions may consist of a pure rare earth or yttrium or mixtures thereof. The recovery of the sequestering agent by mineral acid addition may be carried out by adjusting the etfiuent solution by addition of a suitable mineral acid to a pH of l. The precipitated sequestering agent is removed by filtration. Preferably, a strong mineral acid is used such as nitric, hydrochloric or sulfuric. With the method of the present invention permitting use of higher concentrations of sequestering agent, :the method of recovery and reuse thereof is greatly simplified. It has been found that as high as 90% to 95% of the sequestering agent can be recovered for reuse.

While multiple column operation has been described, it will be appreciated that single column operation is possible. In using a single column, the retainer ions may be transferred into the column in such a manner that a retainer bed of appropriate depth is formed at the bottom of the column. The resin loaded with the mixture to be purified is loaded in the column to form a uniform bed on the top of the retainer resin zone. Elution then proceeds in the normal manner as described above and the eluant solution is collected as fractions containing pure elements and cross contamination bands. The cross contamination bands may be used in forming the rare earth complex salts in the eluting solution with this procedure eliminating the necessity of separate handling of the cross contamination bands and also permitting the buildup of band lengths of the less abundant elements so that higher purity is obtained.

While the use of a sulfonated polystyrene cation exchange resin such as Amberlite IR-lZO is preferred, any other suitable cation exchange resins may be used. By way of example, phenolic methylene sulfonic type resins and the nuclear sulfonic type resins may be used. A specific resin is a hydrocarbon-polymer-type cation exchange resin containing nuclear sulfonic acid groups prepared in accordance With the method described in U.S. Patent No. 2,366,007.

Obviously certain modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims I claim:

l. In an ion exchange system for separating and purifying rare earth and yttrium product ions from mixtures thereof, said system including a plurality of operatively interconnecting zones arranged for selective isolation successively ot' at least one of said zones from the others without interruption of ion exchange and separation in said other zones and in which each of the zones contains a bed of solid cation exchange medium, the improvement which comprises:

(l) establishing a number of successive separation Zones by loading the solid beds in said zones with quantities of a solution containing a mixture of the ions Which are to be separated and purified, said ions being selected from the group consisting of rare earth and yttrium ions,

(2) establishing the next successive zone as a retainer zone by loading the solid bed therein with quantities of a solution containing a mixture of retainer ions selected from the group consisting of rare earth and yttrium ions, the retainer ions having an effective atomic number at least as high as the highest effective atomic number of the ions in the mixture loaded in said separation zones,

(3) establishing ion exchange eluting solution sequestering agent comprising an aqueous solution containing a rare earth complex of ethylenediamine tetraacetate anions, the ions in said ion exchange eluting solution having an effective atomic number no higher than the lowest effective atomic number of the ions in the mixture loaded in said separation zones andltie solution having a pH ranging from about 2.5 to

(4) passing said eluting solution successively through said separation zones whereby the eluting solution absorbs the ions originally loaded into the separation zones with a consequent displacement 0f the rare earth ion content of the eluting solution into the solid beds in the separation zones,

(5) passing the resultant modified eluting solution through the retainer zone to effect therein an ion exchange in which the retainer ions displace the ions previously absorbed by the eluting solution with the latter ions becoming associated with the solid bed in the retainer zone, and

(6) continuously acidifying the liquid medium eifiuent exiting from the retainer zone to separate an aqueous solution of the retainer ions from the sequestering agent,

(7) passing the separated sequestering agent to an eluting solution preparation and supply zone for recycle through said separation zone, and

(8) separating the desired separated and purified rare earth and yttrium product ions from association Y e it with thessolid bed and recover/ingv` the saine'. bygion exchangefwith eluting solutionfrom said prepara- .tion and supply zone.

2. The method of Vclaim Vl whereinthe sequestering 'agent is present in the eluting solution at concentrations of as high asabout 10%. v n t 3. In an ion exchange'system for. separating and purh ensmsg tion Vzone prior to preparationof said first separation fying rare earth and yttrium product ionsY from mixtures Y thereof, said systernincluding Ya .plurality of operatively interconnected Yzones arranged' for selective isolation. successively of. atleast` one of said zones fromithe others without interruption of` ion exchange Vand separation yin said other zones and in which each of the Zones contains a bed of Vsolid cationv exchange medium, theimprovement which comprises: v Y` 'Y e (1) establishing a number of successive separation zones by loading the solid beds'in said zonesffwithY quantitiesV of a solution containing a mixture .ofthe ionswhich are to be 'separatedandpuriiied said ions being selected 'from the group, consisting ofA rare earth andryttrium'ions, f (2) establishing the next successive zone as. a retainer zone by loadingthe solid bed therein with a mixture Vof retainerions selected from the group coni sisting of rare earth and kyttriu'm ions, the retainer ions vhaving an effective atomic number at least Yas highasthe highest effective atomic' number of the ionsin the mixture loadedin saidsepa-rationzones,

zone as a new retainerzone, said introduction occurring in reverse ilow directionl to iiuidize the bed therein and striplthe'same of selected separated ionsv adequate to form the rare earth complex andfv prevent .the formation yof an yinsoluble acid complex in saidV elutingsolution earths andyttrium-froml mixtures thereof which comprises: Vloadinga solution cation exchange medium with a lsolution containing Ya .mixture-to be `separated and concentrated, passinga liquideion `exchange medium sequestering agent comprising anaqueous solution containing a rare earth complex of ethylene diamine tetraacetate anions throughsaid. solution medium, said liquid medium including therein'selected ions-having an eiectiveatomic number no higherthanthe lowesteiective atomic num- `ber of therare earth and yttrium ions tovbe separated Y and concentrated for preferential ion exchange with said (z3)`establishing an ion exchange eluting solutionse questeringagent comprising an aqueous` Ysolution containing a rare earth complex of vethylenediarnine tetraacctate anions, thevanions, in said ion exchange eluting solution having an elfective atomic number no higher than v.the lowest effective atomic number of the ions in theirnixture loaded in saidseparation having a pI-I ranging fromv zones and the solution about 2.5 to 4.5,

(4)passing saidv eluting s olutionsuccessively through said separationr zones `whereby `the eluting solution absorbs the ions originally loaded intothe separation zones with a consequent v displacementV of therareiearthion content ofrvtheV elutingsolution into'V the solid bedsin theseparation fzones,

(5) passing the resultant modied `'eluting solution through the yretainer zone -to eii'ect therein an .ion exchange in .which the retainer ions displacethe ions 4previously absorbedvin the elutingf solution with the latter ions'becoming-associated with the s olidfbed'v in the retainer zone,

(6) continuously acidifying the liquid medium efluent' exiting from the retainer zone to separate an ,aqueous solution of the retainer ions from the sequestering agent,

(7) passing the separated sequestering agent to anYK eluting solution preparation and `supply zone-'for recycle through said separation zones,`

(8) disconnecting the iirst separation zone without i interrupting the delivery of liquid to' vthe remaining zones, Y n (9) loading the bed of said disconnected yzone with the retainer-ions separated yin (6) to form a new retainer zone for reconnection with'the separation:V

zones toprovide for continuous operation ofV said troducing the liquid rnediurn leaving said preparation and. supply zone in ,(6) intoA said disconnected'iirst ,separa-m said solid medium.

ion-loaded solid medium, separating the resulting etluent into'sequestering agent and liquid` fractions of concentrated ion containing lportions thereof, Aandlseparating the ion concentratestherefrom,y the imrpovement which `comprises continuously regenerating saidion exchangevliquid medium by passingdthevcomplex-free sequestering agent recovered fromV said effluent in Areverse flow through 7. In an ion exchange systemfor separating and purifying rare earthV and yttriumY-product ions -frommixtures thereof, said system including a plurality of operatively interconnected beds of-solid Y, cation exchangeresin arranged for selective isolationof atleast oneof said'beds f from the others withoutinterruption of-ion exchange in said other beds, the improvement which comprises.:

(1)` establishing at least one of said `be'cls as a-separation zone by loadingstheV resin therein with .quantifties of a solution containing a mixtureof the ions Vwhichvare to Vvbe separated and puried, saidions lbeing selected fromthe group consisting of vrare earth and yttrium tions,4V (2) establishing the next successive bed' as a retainer zone byloading the resin thereinwith Vquantities of .a solution; containing a mixture of retainer ions selected from the group consistingof rare earth and y yttrium ions, the retainer vions having an effective atomicnumber Vatleast as high as. the yhighestveiiective atomic numberof the ions in themixturefloaded Y in saidseparation zone,` (3) establishing an lion exchange eluting solution sequestering agent comprising 1an aqueous solution of the ammonium, salt ofk ethylenediarnine.tetraacetic acid',.said solution havinga pHj ranging from about 2.5 to 4.5, n y l(4).;passingr said eluting solution through. said separation Vzone wherebyfthe eluting solution absorbs the ionsnioriginally loaded yinto the separation zones with a consequent deposition ofthe ,arnmoniumion of the eluting solution onto the resin inthe separation zone, y y ,(5) passing the resultant vmodified eluting solution through the Aretainerzoner to elect Vtherein 4an ion exchange` @in which the retainer ions displace the iOns previouslyV absorbed by the eluting solution in the separation zonev with the latter ions becoming associated with thesolid\bed in the retainer Y2611, V@(6) continuously treating theliquidjeluent exiting lfrom theV retainer zoneQwithvrnineralacid to separate 13 the sequestering agent from the aqueous solution of retainer ions,

(7) passing the thus separated sequestering agent through an ion exchange liquid medium preparation zone,

(8) disconnecting the first bed in the separation zone Without interrupting the delivery of eluting solution to the remaining beds,

(9) passing the liquid medium leaving the preparation zone in (7) in reverse flow through said disconnected rst bed to regenerate ion exchange eluting solution, thereafter,

(10) passing the aqueous solution of retainer ions obtained in (6) in reverse flow through said disconnected first bed to load the resin therein with said ions and establish a new retainer Zone bed, the aqueous eiuent being discarded, and

(11) recovering the desired product ions from the first retainer zone by passing an ion exchange liquid medium comprising the ammonium salt of ethylenediamine tetraacetic acid in reverse flow therethrough, and treating the liquid effluent exiting therefrom with mineral acid to separate the sequestering agent and leave a solution of the desired product ions.

References Cited in the tile of this patent UNITED STATES PATENTS 2,539,282 Speeding et al. Jan. 23, 1951 2,694,681 Bray et al Nov. 16, 1954 2,798,789 Speeding et al. July 9, 1957 

1. IN AN ION EXCHANGE SYSTEM FOR SEPARATING AND PURIFYING RARE EARTH AND YTRIUM PRODUCT IONS FROM MIXTURES THEREOF, SAID SYTEM INCLUDING A PLURALITY OF OPERATIVELY INTERCONNECTING ZONES ARRANGED FOR SELECTIVE ISOLATION SUCCESSIVELY OF AT LEAST ONE OF SAID ZONES FROM THE OTHERS WITHOUT INTERRUPTION OF ION EXCHANGE AND SEPARATION IN SAID OTHER ZONES AND IN WHICH EACH OF THE ZONES CONTAINS A BED OF SOLID CATION EXCHANGE MEDIUM, THE IMPROVEMENT WHICH COMPRISES: (1) ESTABLISHING A NUMBER OF SUCCESSIVE SEPARATION ZONES BY LOADING THE SOLID BEDS IN SAID ZONES WITH QUANTITIES OF A SOLUTION CONTAINING A MIXTURE OF THE IONS WHICH ARE TO BE SEPARATED AND PURIFIED, SAID IONS BEING SELECTED FROM THE GROUP CONSISTING OF RARE EARTH AND YTRIUM IONS, (2) ESTABLISHING THE NEXT SUCCESSIVE ZONE AS A RETAINER ZONE BY LOADING THE SOLID BED THEREIN WITH QUANTITIES OF A SOLUTION CONTAINING A MIXTURE OF RETAINER IONS SELECTED FROM THE GROUP CONSISTING OF RARE EARTH AND YTRIUM IONS, THE RETAINER IONS HAVING AN EFFECTIVE ATOMIC NUMBER AT LEAST AS HIGH AS THE HIGHEST EFFECTIVE ATOMIC NUMBER OF THE IONS IN THE MIXTURE LOADED IN SAID SEPARATION ZONES, (3) ESTABLISHING ION EXCHANGE ELUTING SOLUTION SEQUESTERING AGENT COMPRISING AN AQUEOUS SOLUTION CONTAINING A RARE EARTH COMPLEX OF ETHYLENEDIAMINE TETRAACETATE ANIONS, THE IONS IN SAID ION EXCHANGE ELUTING SOLUTION HAVING AN EFFECTIVE ATOMIC NUMBER NO HIGHER THAN THE LOWEST EFFECTIVE ATOMIC NUMBER OF THE IONS IN THE MIXTURE LOADED IN SAID SEPARATION ZONES AND THE SOLUTION HAVING A PH RANGING FROM ABOUT 2.5 TO 4.5, (4) PASSING SAID ELUTING SOLUTION SUCCESSIVELY THROUGH SAID SEPERATION ZONES WHEREBY THE ELUTING SOLUTION ABSORBS THE IONS ORIGINALLY LOADED INTO THE SEPARATION ZONES WITH A CONSEQUENT DISPLACEMENT OF THE RARE EARTH ION CONTENT OF THE ELUTING SOLUTION INTO THE SOLID BEDS IN THE SEPARATION ZONES, (5) PASSING THE RESULTANT MODIFIED ELUTING SOLUTION THROUGH THE RETAINER ZONE TO EFFECT HEREIN AN ION EXCHANGE IN WHICH THE RETAINER IONS DISPLACE THE IONS PREVIOUSLY ABSORBED BY THE ELUTING SOLUTION WITH THE LATTER IONS BECOMING ASSOCIATED WITH THE SOLID BED IN THE RETAINER ZONE, AND (6) CONTINOUSLY ACIDFYING THE LIQUID MEDIUM EFFLUENT EXITING FROM THE RETAINER ZONES TO SEPARATE AN AQUEOUS SOLUTION OF THE RETAINER IONS FROM THE SEQUESTERING AGENT, (7) PASSING THE SEPARATED SEQUESTERING AGENT TO AN ELUTING SOLUTION PREPARATION AND SUPPLY ZONE FOR RECYCLE THROUGH SAID SEPARATION ZONE, AND (8) SEPARATING THE DESIRED SEPARATED AND PURIFIED RARE EARTH AND YTRIUM PRODUCT IONS FROM ASSOCIATION WITH THE SOLID BED AND RECOVERING THE SAME BY ION EXCHANGE WITH ELUTING SOLUTION FROM SAID PREPARATION AND SUPPLY ZONE.
 6. IN THE METHOD OF SEPARATING AND CONCENTRATING RARE EARTHS AND YTRIUM FROM MIXTURES THEREOF WHICH COMPRISES: LOADING A SOLUTION CATION EXCHANGE MEDIUM WITH A SOLUTION CONTAINING A MIXTURE TO BE SEPARATED AND CONCENTRATED, PASSING A LIQUID ION EXCHANGE MEDIUM SEQUESTERING AGENT COMPRISING AN AQUEOUS SOLUTION CONTAINING A RARE EARTH COMPLEX OF ETHYLENE DIAMINE TETRAACETATE ANIONS THROUGH SAID SOLUTION MEDIUM, SAID LIQUID MEDIUM INCLUDING THEREIN SELECTED IONS HAVING AN EFFECTIVE ATOMIC NUMBER NO HIGHER THAN THE LOWEST EFFECTIVE ATOMIC NUMBER OF THE RARE EARTH AND YTRIUM IONS TO BE SEPARATED AND CONCENTRATED FOR PREFERENTIAL ION EXCHANGE WITH SAID ION-LOADED SOLID MEDIUM, SEPARATING THE RSULTING EFFLUENT INTO SEQUESTERING AGENT AND LIQUID FRACTIONS OF CONCENTRATED ION CONTAINING PORTIONS THEREOF, AND SEPARATING THE ION CONCENTRATES THEREFROM, THE IMPROVEMENT WITH COMPRISES CONTINOUSLY REGENERATING SAID IO N EXCHANGE LIQUID MEDIUM BY PASSING THE COMPLEX-FREE SEQUESTERING AGENT RECOVERED FROM SAID EFFLUENT IN REVERSE FLOW THROUGH SAID SOLID MEDIUM. 